Enzon is involved in the development of therapeutic enzymes for human and veterinary use. Many enzymes have shown effectiveness as anticancer agents on initial injection, but their immunogenicity and short plasma halflife have prevented exploitation of their potential. Enzon will modify two glutaminaseasparaginases and a histidase by our patented process to produce enzymepolyethylene glycol (PEG) conjugates with vastly improved plasma halflives and greatly reduced immunogenicities. These PEGenzymes can be injected repetitively so that their full therapeutic potential can be utilized. Enzon will perform plasma half-life and initial toxicological studies on the three PEGenzymes. Our longterm objective is to obtain investigative New Drug members and commence clinical studies. These enzymes are the forerunners of a larger group of nonessential and essential amino acid - degrading enzymes that will be developed as therapeutic agents for various types of cancer.